Railroad brake shoes



Nov. 3, 1959 w. s. FRAULA ETAL 2,911,074 1 RAILROAD BRAKE SHOES FiledAug. 10, 1956 INVENTORS.

W. SCOTT FRAULA ERWIN R. KNAUER BY RAYMOND E. SPOKES flcllaa/ul WATTORNEIYS ,terial and the metal back structure.

United Sta es Patent O P RAILROAD BRAKE SHOES William S. Fraula,Ridgewood, and ,Erwin R. Knauer, Woodcliif Lake, N.J., and Raymond E.Spokes, Ann

Arbor, Mich., assignors to American Brake Shoe Company, New York, N.Y.,a corporation of Delaware Application August 10, 1956, Serial No.603,407 1 Claim. (Cl. 188-251) railroad industry comprises a cast ironbody having a substantial thickness and having a braking surface whichis curved to correspond generally to the curvature of a railroad car orlocomotive wheel. A supporting plate or strip of rolled steel isfrequently included in the back of the cast iron brake shoe as areinforcement for the cast iron body and, to a certain extent, serves tohold the brake shoe body together if it becomes cracked or otherwisefractured; usually, the brake shoe body is cast around the supportmember to form a unitary structure. A substantially different type ofbrake shoe which has been considered for use on railroad cars andlocomotives comprises a molded composition body which may be supportedupon a steel backing plate; this steel backing structure is in somerespects similar to the support member of the cast iron type of shoe, inthat it lends strength and rigidity to the brake shoe body. In thecomposition type brake shoe, the support lugs and other elements formounting the shoe upon a brake head are formed as a part of or aremounted upon the steel supporting back; in the cast iron type of shoe,the mounting lugs, toe guides, and the like may be cast as a part of thebrake shoe body or may be formed as steel members affixed to theaforementioned steel reinforcing strip.

The composition type brake shoe provides substantially higher retardingforce per unit area than the standard cast iron shoe, since it aifordsaconsiderably higher coefficient of friction when brought into contactwith the wheel of a car or locomotive than may be obtained with a castiron shoe. Ingeneral, it may be stated that the cast iron shoe is ahigh-pressure low friction device, Whereas the composition shoe is ahigh-friction. low-pressure device. Accordingly, the'composition shoemay be operated at substantially lower braking pressures than the castiron shoe and permits utilization of smaller brake cylinders. known inthe art, has several serious disadvantages which have precludedwidespread adoption of this type of shoe for railroad service. Among thedifficulties presented with the composition shoe, a principal onehas'been the tendency of the composition body toseparate from the metalback or support structure under even relatively mild braking conditions.In particular, this difliculty may be attributed to the difference inthe thermal coefiicients of expansion of the brake shoe composition ma-In addition, the composition brake shoe body may be separated from itssupporting metal back as a result of forces tending to flex thebrakeshoe, which are frequently encountered in railroad service; these sameflexural forces may also tend ;to fracture the composition brakeshoebody. Moreover,

The composition type shoe, however, as

Patented Nov. 3, 1959 the relatively severe vibration frequentlyencountered in railroad operations often tends to crack the compositionbody/ or to detach the body from its metal backing struc-' ture. Q 1

One proposal which has been advanced as a means to strengthen thecomposition body of a railroad brake shoe contemplates the incorporationof one or more layers ofexpanded metal .into the brake shoe body as areinforcement; the expanded metal is embedded in the compositionmaterial in a portion thereof closely adjacent the metal backingstructure. Brake shoes incorporating this type of expanded metalreinforcement, however, have also exhibited certain disadvantages. --Forexample, the expanded metalreinforcing strip tends to create adiscontinuity in the composition body and, when the body is subjected tothe stresses of braking service, may cause the body to fracture orseparate adjacent the reinforcement. In addition, conventional moldingand processing techniques sometimes fail to fill the interstices of theexpanded metal completely with composition material; as a consequence,the brake shoe body is "effectively weakened instead of beingstrengthened by the presence of the expanded metal.

Itis an object of the invention, therefore, to overcome or substantiallyminimize the'above-noted disadvantages of previously knowncomposition-type railroad brake shoes by resort to a specific method ofmanufacturing a reinforced composition shoe. 7 I

A further object of the invention is the provision 'of a new andimproved railroad brake shoe structure, comprising a metal back, acomposition body, and a meshtype'reinforoing structure embedded in thecomposition body, which inherently eliminates or minimizes thedisadvantages of known shoes noted above.

Accordingly, in one aspect the invention is directed to a railroad brakeshoe of the type comprising a composition body having a predeterminedlength, width, and longitudinal curvature supported upon a metal back.In accordance with the inventive method, a metal brake shoe backingstructure is fabricated with a predetermined length, width, andlongitudinal curvature approximately corresponding to the length, width,and curvature of a composition brake shoe body. This metal backingstructure is deposited in a mold with the concave surface of thebackingstructure facing inwardly in that mold. A sheet of expandedmetal, preferably having approximately the same length, width, andlongitudinal curvature as the backing structure, is packed or otherwisecoated with an uncured composition material and is then deposited withinthe brake shoe mold adjacent theconcave surface of the metal backingstructure. The composition-packed expanded metal may be depositeddirectly on the backing structure surface or an additional layer ofuncured composition material may be interposed between the expandedmetal layer and the backing structure. Subsequently, the mold is filledwith an uncured composition material, after which all of the compositionmaterial is subjected to a curing treatment to harden the compositionmaterial.

In another aspect, the invention is directed to a railroad brake shoecomprising a metal back structure having a predetermined length, width,thickness, and longitudinal curvature; this metal back structure isbonded on its concave surface to a brake shoe formed from a firstcomposition material and having corresponding-dimensions but with athickness substantially greater .than the thickness of the backstructure. A reinforcing member, comprising a metal mesh having alength, width, and curvature approximately corresponding to the backstructure is embedded in the composition brake body at a positionclosely adjacent the metal back structure. A

bond coating, which comprises a second composition material, completelycovers this reinforcing member and is utilized to bond the reinforcingmesh to the brake body.

Other and further objects of the present invention will be apparent fromthe following description and claims and are illustrated in theaccompanying drawing which, by way of illustration, shows a preferredembodiment of a brake shoe construction in accordance with the method ofthe invention. The principles of the invention are set forth fully inthe description and claim; other embodiments of the invention embodyingthe same and equivalent principles may be used and structural changes inthe devices to whichthe inventive method is applied may be made asdesired by those skilled in the art without departing from the inventionand the purview of the appended claim.

In the drawings:

Fig. 1 is an elevation view, partly in cross section, of acomposition-type railroad brake shoe including an expanded metalreinforcing element;

Fig. 2 is a plan view of the brake shoe illustrated in Fig. 1;

Fig. 3 is a plan view of an expanded metal reinforcing memberincorporated in the brake shoe of Fig. 1;

Fig. 4 is a cross sectional view taken along line 4-4 in Fig. 3,illustrating the expanded metal reinforcing element at an intermediatestage in the inventive process;

Fig. 5 is a cross sectional view, taken along line 5-5 in Fig. 2,showing the location of the expanded metal reinforcing element in thebrake shoe body;

Fig. 6 is a cross sectional view of the brake shoe taken along line 66in Fig. 1; and

Fig. 7 is a detail sectional view taken along line 7-7 in Fig. 2. e I

The brake shoe 20 illustrated in Fig. 1 comprises a metal back structureincluding a support member 21 which is utilized to support a moldedcomposition body 22 and to mount brake shoe 20 upon a brake head (notshown). Composition body 22 has a predetermined length, width, andthickness and further has a predetermined curvature along its lengthapproximately corresponding to the curvature of the railroad car orlocomotive wheel with which it is to be employed. The length and widthof metal support equal to the corresponding overall dimensions ofcomposition body 22 and the metal support member has essentially thesame longitudinal curvature as the composition brake shoe body. Itshould be understood that the dimensional correspondence between supportmember 21 and composition body 22 need not be exact, although majorvariations are not desirable; for example, in some applications it maybe necessary or desirable to extend the length of composition body 22somewhat beyond the end of metal support member 21 or to make itsomewhat wider than the metal back structure.

Apair of longitudinal flanges 23 and 24, which are best shown in Figs.1, 5 and 6, may be aflixed to the edges of metal support member 21 andextend from the support member into engagement With the sides of thecomposition body. These flanges are preferably formed as an integralpart of the metal support member in order to achieve maximum strengthand manufacturing economy in the back structure. The efiective height offlanges 23 and 24 is preferably made substantially smaller than thethickness of composition body 22 in order to prevent the metal backingstructure from contacting the wheel or other surface to which the brakeis applied, since the steel from which support member 21 and flanges 23and 24 are preferably fabricated could score the wheel or might becomewelded to the wheel at the-extreme temperatures encountered in railroadbraking service. As shown in Figs. 1 and 2, a pair of end stops 25 and26 are formed at one end of support member 21 and extend abovetheconcave surface 27 of the support member to engage a brake head; anadditional pair of end stops 28 member 21 are approximately and 29 areprovided at the opposite end of support member 21. A pair of toe guides30 and 31 are formed at opposite ends of the support member; the endstops and toe guides are most economically fabricated as an integralpart of support member 21 by punching or similar manufacturingtechniques. A center attaching lug 32 is mounted on support member21 byclinching or any other suitable method; the usual keyway 33 is formed inthe center attaching lug as indicated in Fig. 6.

Individual portions of support member 21 are punched out at distributedlocations on the support member to form a plurality of individual metalanchor elements 35 extending from the concave surface 34 of supportmember 21 into composition body 22, as best indicated in Figs. 5 and 6.These projections or anchor elements serve to interlock the compositionbody and metal backing structure of the brake shoe to each other. As inthe case of flanges 23 and 24, anchor. elements 35 should have aneffective height. substantially smaller than the thickness ofcomposition body 22 to prevent the metal anchor elements from contactingthe wheel during braking service. In addition, composition body 22 maybe further interlocked with support member 21 by means of a plurality ofopenings 37 in support member 21 immediately adjacent and extending intoa portion of flanges 23 and 24 (see Fig. 7); portions of the compositionbody extend into openings 37 to provide further anchorage points withsupport member 21.

The metal backing structure of brake shoe 20 comprising support member21, the end stops, the toe guides, and the longitudinal flanges, alongwith anchor elements 35, is preferably formed from steel, eitherhot-rolled or cold-rolled; hot-rolled steel is.usually preferred. Theconstruction of brake shoe 20, as thus far described, providessubstantially improved characteristics with respect to adherence of thecomposition body to the steel backing structure when compared withpreviously known devices and is also substantially more resistant tofracture; this construction is described and claimed in the copendingapplication of E. E. Caton et al., Serial No. 606,869, filedconcurrently herewith and assigned to the same assignee as the presentinvention. In some applications, however, it is desirable to strengthenthe brake shoe further and to provide even greater adherence between themetal backing structure and composition body. For this purpose, and inaccordance with the invention, a mesh-type reinforcing strip or. sheet40 is incorporated in the brake shoe, as indicated in Figs. 1,5 and 6,being embedded in composition body 22 at a position closely adjacentsupport member 21. Reinforcing strip 40 is preferably formed fromexpanded metal and is shaped to conform to the dimensions and curvatureof metal back 21. The present invention is based upon the discovery thata particular method of incorporating expanded metal reinforcing member40 in the brake shoe is highly advantageous and effectively avoids thedisadvantages encountered in previously known composition type brakeshoes incorporating reinforcing elements of this general yp Inmanufacturing brake shoe 20, and in accordance with the'invention, thefollowing method is followed: the metal back structure comprisingsupport member 21, the toe guides, end stops, flanges, center lug, andthe like is first fabricated as a complete unit having a predeterminedlength, width, and longitudinal curvature approximately corresponding tothe length, width, and curvature desired for the composition brake shoebody. This metal backing structure is then deposited in a suitable brakeshoe mold with the concave surface 34 of the backing structure facinginwardly in the mold. A sheet of expanded metal 40, illustrated in Fig.3, is shaped to conform in curvature to the curvature of backing member21, as indicated in Fig. 4; preferably, expanded metal sheet 40 has alength and width closely approximating the 4 length andwidth of thebrake shoe support member.

, Expanded metal member 40 isthen coated with an uncured compositionmaterial; in some instances the reinforcing strip may be filled andpacked completely with the composition as indicated at 41 in Fig. 4.Composition material 11 may be packed into the expanded metal underpressure in order to avoid any air pockets or discontinuities in thecomposition material filling the expanded metal. In other instances, asset forth in detail hereinafter, the composition material may be appliedto reinforcing mesh 40 by spraying, painting, or similar techniques. i 1v Expanded metal reinforcement 40, after coating or packing withcomposition material 41, is then deposited within the brake shoe moldadjacent concave surface 34 of support member 21. It may be desirable tofirst deposit a layer of composition material upon surface 34 before thepacked expanded metal is inserted in the mold, depending upon thethickness of the coating or packing layer 41. The brake shoe mold isthen .filled with uncured composition material, which may be ofdifferent constituency from coating 41, after which all of thecomposition material is subjected to a curing treatment to harden thecomposition material. This curing treatment entails the application ofheat and pressure to the mold to solidify and harden the compositionmaterial, as described in greater detail hereinafter.

The composition material employed in manufacturing brake shoe 20 may beof any type suitable for railway braking service, but preferablycomprises a comminuted friction material, selected from the sillimanitegroup and related aluminum silicates, distributed in a heat-stablerubber binder. The friction material, which may include kyanite,sillimanite, andalusite, mullite, topaz, and/ or dumortierite,preferably comprises about ten parts by weight of the composition. Thebinder may comprise any heat-stable synthetic or natural rubber; forexample, Buna-S synthetic rubber either with or without an additionalliquid polymer has been found quite satisfactory for this purpose.The'invention may also be applied to a brake shoe composition employingphenolic or other resin binders, although an elastomer-base compositionof the type noted above, which is described and claimed in the copendingapplication of R. E. Spokes et al., Ser. No. 491,510, filedMarch l, 1955and assigned to the same assignee as the present inventio is muchpreferred because of its superior characteristics with respect to heatand shock resistance. Moreover, the Spokes et al. composition affords afavorable ratio of wet to dry coefficients of friction, a highlydesirable characteristic in railroad service. In addition to the mineralfriction material, the composition may include further friction materialin the form of cast iron particles or other suitable material.

Several different specific processes incorporating the inventive concepthave been found to be most advantageous, as compared with previouslyknown techniques; the particular examples set forth hereinafter areintended primarily as an illustration of individual applications of theinvention and are not to be construed as limiting the invention to thespecific coating compositions set forth.

therein. For convenience, and to assist in understanding the applicationof the invention, the various steps of the processes set forth in thespecific examples are separately designated as Steps A, B, etc.;,nevertheless, as will bequite apparent from a consideration of theexamples themselves, the sequence of steps in the examples is notparticularly critical in most instances and may be subject to widevariation without in any way departing from the invention.

Example I Step A.A metal brake shoe backing structure is fabricated witha predetermined length, width, and longitudinal ing, painting,

tially similar to that described above in connection with Figs. 1 and 2and may include suitable mounting lugs.

Step B.A mesh-type reinforcing strip is cut to a size approximatelycorresponding to the length andwidth of the metal backing structure andis shaped to have a longitudinal curvature corresponding to that of themeta l backing structure; the shaping operation may be readily performedin a punch press or similar apparatus. The reinforcing strip ispreferably fabricated; from expanded metal as illustrated in Fig. 3; I

Step C.-The expanded metal or other mesh reinforcing strip is coatedwith a rubber-resin cement possessing superior bonding qualities withrespect to the metal. This cement, which comprises an uncured coatingcomposition,

preferably includes a combination of a rubber, a thermosetting resin,and a suitable solvent. A preferred composition which afiords excellentresults is as follows:

'Solids: Parts by weight Buna-N 50 Phenol aldehyde 50 The rubber andresin solids are dissolved in a suitable solvent; methyl ethyl ketonehas been found quite suitable for this purpose, although other organicsolvents may alsobe employed. The relative weights of the Buna-Nbutadiene-acrylonitrile) rubber and the thermosetting resin are notparticularly critical and may be varied within relatively broad limits.The ratio of solids to solvent I may be adjusted as desired to suit theparticular technique selected for applying the uncured composition tothe reinforcing mesh; thismay be accomplished by spraydipping, or by anyother method adapted to coat the entire mesh with the composition. Itwill be appreciated that the cementing phenomenon involved is physicalin nature and that other cements having similar properties may beemployed.

Step D.The concave or under surface of the metal back structure iscoated with the cement set forth in Step C or With a similar uncuredcomposition by spraying, painting, etc. It should be noted that althoughthis step in the inventive process is highly desirable and improvesadherence of the brake shoe body to the metal backing structure, themajor benefits of the invention may be obtained without its use.

Step E.The metal backing structure is deposited in a mold with theconcave surface thereof facing inwardly in the mold and thecomposition-coated mesh reinforcing element is located adjacent theconcave surface of the metal back. It may be desirable to fill the metalbacking structure with a relatively thin layer of the compositionmaterial to be employed as the brake shoe body before the expanded metalreinforcing element is placed within the mold.

Step F .The mold is filled with an uncured composition material suitablefor braking service, preferably the composition described and claimed inthe aforementioned Spokes et a1. application. 1

Step G.All of the composition material is subjected to heat and pressureto cure and harden the material and form the completed brake shoe. Itshould be noted that the cement or coating composition is cured in thisstage of the process along with the composition which forms the brakingsurface of the shoe and that the resin included in the cement isadvanced'or cured to a relatively hard unflexible state and is bonded toboth the composition body of the shoe and the metal reinforcing strip.The rubber in the coating composition imparts a certain degree offlexibility to the coating composition so that it is able to withstandthe flexural stresses to which the shoe is subjected during brakingservice.

Example II Steps A and B, in this example, are essentially similar tothecorrespondingly designated steps of Example I. Step C'.-The metalreinforcing mesh is coated or "7 packed with an uncured composition ofthe following constituency:

Constituents: Parts by weight i Rubber cement 6.00 Sulphur 0.21 Liquidphenol aldehyde resin 13.00 Barytes 6.55 Petroleum 'solvent (naphtha)2.00 Asbestos (Canadian Std. 7D) 26.70 Asbestos (Canadian Std. R) 20.90Methyl or ethyl alcohol 1.00

The rubber cement included in this particular composition may compriseone part Buna S rubber, three and one half parts reclaimed rubber, andfour parts petroleum solvent by Weight. The composition, after meshing,is extruded, and excess solvent is removed by oven drying at 150 F. fortwenty hours before using.

jfStep D.,The concave surface of the metal backing structure is filledwith a relatively. thin layer of the uncured composition set forth abovein connection with Step C.

The last three Steps E, F, and G in this example are essentially similarto those setforth above in connection with Example I.

It must be understood that the two examples set forth above are ,notmutually exclusive. For example, the metal backing structure and thereinforcing mesh of the :brake shoe may be coated with the compositiondescribed in Example I by spraying, painting, etc. and may also befurther coated or packed in accordance with the technique set forth inExample II in fabricating the shoe. On the other hand, it may bedesirable to fill the backing structure with a special composition as inStep D of Example III and to coat the reinforcement with a cement asdescribed in Step C of Example I without recourse to Steps C and D ofthe example. Other combinations of the 'two'examples are also possible.It must be borne in mind, however, that in every instance the mesh mustbe pre-coated or pre-packed with an uncured composition material beforeit is inserted into the mold and before the mold is filled with thecomposition which is to afford the braking surface.

Composition-type shoes constructed in accordance with theabove-described inventive methods exhibit markedly better resistance tofracture from either the flexural or vibrational forces encountered inrailway braking service.

The pre-coating or packing technique avoids the serious disadvantages ofexpanded metal reinforcements as previously applied to composition typeshoes and assuresa substantially uniform composition body free ofweakness along the plane of expanded metal. In addition, brake shoesconstructed in accordance With the inventive technique exhibitsubstantially better adherence of the composition body to the metalbacking structure than is obtained in unreinforced shoes.

Hence, while we have illustrated and described the preferred embodimentsof our invention, it is to be understood that these are capable ofvariation and modification, and we therefore do not wish to be limitedto the precise details set forth, but desire to avail ourselves of suchchanges and alterations as fall within the purview of the followingclaim.

We claim:

A railroad brake shoe comprising: a metal back-structure having apredetermined length, width, thickness, and longitudinal curvature; afirst bond coating, comprising a first composition material covering theinternal surface of said back structure; a brake body, formed from asecond composition material different from said first compositionmaterial; bonded to the concave surface of said metal back structure bysaid first bond coating and having a length, width and curvatureapproximately correspond.- ing to said metal back structure and athickness substantially greater than said back structure; a reinforcingmember, comprising a metal mesh having a length, Width and curvatureapproximately corresponding to said back structure, embedded in saidcomposition brake body at a position closely adjacent said metal backstructure and spaced therefrom by a layer of said second compositionmaterial; and a second bond coating, comprising said first compositionmaterial, completely covering said reinforcing member, for bonding saidreinforcing member to said brake body.

References Cited in the file of this patent UNITED STATES PATENTS1,830,341 Smith Nov. 3, 1931 2,052,808 Spokes Sept. 1, 1936 2,431,393Franklin Nov. 25, 1947 2,702,770 Steck Feb. 22, 1955 2,728,701 WirthDec. 27, 1955 2,746,090 Hoover May 22, 1956

